Linear motion guide units have been extensively applied in recent years between two parts which slide relative to each other in a variety of industrial fields including semiconductor fabricating equipment, various inspection/assembling machines, machine tools, and so on. With the prior linear motion guide units, a carriage for a slider has lengthwise holes which have therein sleeves of porous compact impregnated with lubricant. The balls while rolling through return passages defined within the sleeves are applied with the lubricant, thereby realizing virtual maintenance-free operating conditions for lubrication.
In the commonly assigned Japanese senior Laid-Open Patent Application No. 2001-082 469, there is disclosed a linear motion guide unit in which a slider has a lengthwise through-hole to fit over a sleeve of porous compact of sintered resinous material impregnated with lubricant to provide a return passage. The lubricant is applied for a prolonged interval around the balls while rolling through the return passage. With the linear motion guide unit recited just above, a slider movable relative to a guide rail through more than one rolling elements such as balls has a lengthwise through-hole into which the sleeve of sintered resinous material of porous texture fits to define the return passage to allow the balls to roll through the inside the sintered resinous material. With the prior linear motion guide unit constructed as stated earlier, lubricant impregnated inside the porous texture of the sintered resinous material continues to be applied around the balls while running though the return passage. Thus, load-carrying races are lubricated through the balls, thereby improved in reliability and, therefore, the sliding resistance against the slider is reduced remarkably.
Another commonly assigned Japanese prior Laid-Open Patent Application No. 2013-096 431, discloses a linear motion guide unit in which a porous compact impregnated with lubricant is installed in an end cap in a way exposed to a turnaround passage in the end cap. The prior linear motion guide unit recited above, as shown in FIGS. 18 to 20, comprises a guide rail 1P having a raceway groove 11P extending lengthwise on each longitudinal side 37P of the guide rail, and a slider 2P which fits over or conforms to the guide rail 1P for movement relative to the guide rail. The slider 2P is composed of a carriage 3P having a pair of end caps 4P secured to opposite ends 38P of the carriage. The carriage has a raceway groove 12P lying in opposition to the raceway groove 11P of the guide rail to define a load-carrying race between opposed raceway groove 11P and raceway groove 12P. The carriage has a return passage 22P extending along the load-carrying race. The end caps 4P each have a turnaround passage to connect the load-carrying race and the return passage 22P. The slider 2P has a porous compact 7AP impregnated with lubricant to apply around balls rolling through a recirculating circuit which is made up of the load-carrying race, the return passage and the turnaround passages. Moreover, the slider has an end plate 8P to press the porous compact 7AP into a recess 34 in the end cap 4P. The end cap 4P is composed of an end cap major part 5P and a spacer part 6P. The end cap 4P together with the end plate 8P is secured to the carriage 3P by means of fastening screws 9P which have been driven into threaded holes 47P. With the prior linear motion guide unit constructed as recited earlier, the porous compact 7AP is installed exposed to the turnaround passage to make certainly steady application of lubricant around the balls while rolling through the turnaround passage, realizing a virtual maintenance-free operating condition for lubrication. With the linear motion guide unit constructed as stated earlier, the porous compact 7AP fits in the recess 34P in the end cap major part 5P and the end cap has a slit 33P cut in the outside circular wall surface 23P of the porous compact 7AP. An applicator nose 25P of the porous compact 7AP at a tip end 28P thereof is exposed into the turnaround passage through the slit 33P. The balls while rolling through the turnaround passage along slit edges are brought into rolling contact with the tip end 28P of the porous compact 7AP and coated with the lubricant held in the porous compact 7AP.
In another commonly assigned Japanese senior Laid-Open Patent Application No. 2007-032 724, there is disclosed a linear motion guide unit which is allowed to work with high-speed sliding operation and high tact for long service life with substantial maintenance-free for lubrication. This linear motion guide unit has a heavy load capacity even with its smaller size. To this end, return passages are made in a geometry lying obliquely upwards of load-carrying races. The return passages are apart and spaced away from their associated load-carrying races by a distance less or equal to twice a diametral dimension of a rolling element. End caps are integrally made with spigots, each of which is raised above a surface of the associated end cap facing on the carriage, thereby providing any one of forward and aft ends of the return passage. The spigots communicate with lubricant paths extending from lubricating ports made in the end caps.
In a further another commonly assigned Japanese senior Laid-Open Patent Application No. 2013-040 674, there is disclosed a miniature linear motion guide unit in which a tubular porous compact for a return passage is installed in an outward open recess cut in the carriage and a covering to bear the tubular member is integral with an end cap major part to make the slider compact and simple with cost saving in production. With the miniature linear motion guide unit constructed as stated earlier, the slider is composed of a carriage made up of an upper portion and side bulges extending downward and having the outward open recesses, end caps having turnaround passages, the tubular members lying on the outsides of the side bulges of the carriage, and coverings connected integrally with the end cap major parts to embrace the tubular members in combination with the outsides of the carriage. Lubricant is applied around the balls for rolling elements while the balls roll through the turnaround passages.
With the linear motion guide unit in which the sleeve is used for the return passage, however, as the carriage necessarily has the lengthwise bore larger in diameter than the return passage, the carriage is inevitably made smaller in thickness around the lengthwise bore. This causes a serious problem in mechanical strength of the carriage. To make the porous compact larger in volume, moreover, it is needed to make the end cap longer in the lengthwise direction of the slider. With the prior linear motion guide unit having no lubrication means, more especially a miniature version having the guide rail of around 3 mm in width, it is needed to supply lubricant at regular intervals to provide lubrication between the raceway grooves and the rolling elements, thereby protecting the direct contact of the raceway grooves with the rolling elements. With the prior miniature linear motion guide unit having the guide rail of around 3 mm in width and the sleeve of lubricating material, though it was basically preferable to keep the turnaround passage at the level equal with load-carrying races, the slider could not be made larger in width. In view of construction of the carriage, thus, there was no space on the carriage allowed for making the bore extend along the load-carrying race on the carriage. Moreover, with the miniature linear motion guide unit, the prior lubricant member could not be made large enough to hold ample lubricant therein, which created an issue giving rise to the shortage of lubricant in the endurance test.
With the prior linear motion guide unit, as the slider or the carriage of the slider usually is of a blocky contour having threaded holes lying spaced apart from each other on the widthwise middle zone of the slider, the sidewise opposed bulges of the carriage has spaces which afford to have lengthwise bores to stow the lengthwise sleeves therein, thereby providing the linear motion guide unit of sleeve type.